Research On Calculation Model Of Crack Width Of Steel Lined Reinforced Concrete Penstocks

Under the design internal water pressure of steel-lined reinforced concrete penstocks,the enclosed reinforced concrete usually works with cracks.How to construct a reasonable crack width calculation formula to improve the calculation accuracy has always been one of the research focuses of researchers.In the current relevant codes,the crack width calculation method of ordinary beam concrete structures is still used for the calculation of cracks in penstocks,which will inevitably lead to big difference between the calculated results and the measured values.In view of this,based on the special structural type and stress characteristics of steel-lined reinforced concrete penstocks,the crack width at the outer edge of the penstock was taken as the entry point.Combined with model test and FEM simulation analysis,the stress distribution,radial displacement and cracking mechanism of steel-lined reinforced concrete penstocks were analyzed.The improvement of the crack width calculation formula was carried out so as to effectively control the actual structural cracks.The research results can provide a reference for the revision of domestic steel-lined reinforced concrete structure crack control standards.The specific research content is as follows:(1)Research on mechanical properties and cracking mechanism of steel-lined reinforced concrete penstocks.Through self-made internal water pressure simulation loading device,the model test was carried out,and the stress condition and crack characteristics of steel-lined reinforced concrete penstocks were studied.In terms of stress distribution,it was observed that the loop tensile stress of the steel pipe at the pipe top position was the largest,and the loop tensile stress of the outer steel bar at the pipe waist was the largest.About the crack distribution phenomenon,under step loading,the pipeline first produced radial cracks in the middle of the pipe from the outside to the inside or on the top of the pipe from the outside to the inside.On the distribution of cracks,by step loading,from outside to inside the radial crack was first produced on the top of the middle of the pipe;For crack control,reinforcement ratio remains constant,with fine and dense steel bar can effectively reduce the number of cracks under the pressure of water within the design.(2)Nonlinear finite element analysis of a steel-lined reinforced concrete penstocksmodel.By using ANSYS software,a reasonable finite element analysis model was constructed based on the model test parameters,and the large-scale pipeline model was simulated.Then the simulation results were compared with the model test results.The differences between the finite element analysis results of the square pipe model and the axisymmetric multilayer ring model were analyzed.(3)Improved research on calculation model of crack width of steel lined reinforced concrete penstocks.By combining the results of model tests and finite element analysis,the radial displacement of the outer edge of the pipeline varied significantly,and radial cracks were mainly distributed in the overhanging part of the pipeline.On the basis of Dong’s model,a calculation model was proposed taking the overhanging part of the pipeline as the main computing object with the crack width constraint at the bottom of the pipeline.Based on a numerical example,the rationality of the proposed crack width calculation model was verified.